Conventionally, a light source unit is known which uses an LED (light emitting diode), which is a light emitting element, as a light source. And, such a conventional light unit is disposed in a liquid crystal display device that is a display device, thereby functioning as a backlight unit that illuminates a liquid crystal display panel. In other words, display operation of the liquid crystal display device as a conventional display device is performed by means of light generated by the LED.
Hereinafter, a structure of the conventional backlight unit, which uses the LED as the light source, is described. Here, there are a direct type of backlight unit and an edge light type backlight unit; the backlight unit described hereinafter is the edge light type.
The conventional backlight unit, as shown in FIG. 24, includes at least: a light guide plate 101 that outputs surface light to a liquid crystal display panel (not shown); and a plurality of LEDs 102 that generate the light which is output from the light guide plate 101. The light guide plate 101 is substantially rectangular when viewed from its plate-thickness direction and has: a light introduction surface (a surface for introducing light inside) 101a that is formed of a predetermined side surface; and a light output surface (a surface for outputting the light introduced inside as surface light to the liquid crystal display panel) 101b that is formed of a ceiling surface. Besides, the plurality of LEDs 102 are linearly arranged along the light introduction surface 101a of the light guide plate 101 such that each light emitting surface faces the light introduction surface 101a of the light guide plate 101.
And, in the conventional backlight unit, when light is generated by the plurality of LEDs 102, the light generated by the plurality of LEDs 102 is introduced from the light introduction surface 101a of the light guide plate 101 into an inside of the light guide plate 101. Thereafter, the light introduced into the inside of the light guide plate 101 turns into surface light and is output from the light output surface 101b of the light guide plate 101.
Here, although not shown, a reflection sheet is disposed on a rear surface (a surface opposite to the light output surface 101b) of the light guide plate 101, and an optical sheet is disposed on the light output surface 101b of the light guide plate 101.
In the meantime, in the conventional backlight unit shown in FIG. 24, the light generated by the LED 102 travels spreading radially, so that if a distance between adjacent LEDs 102 is large, dark regions (regions marked by hatching in the figure), into which the light spreads only slightly, occur near the light introduction surface 101a of the light guide plate 101, which cause brightness unevenness. As ways of solving this disadvantage, there are: a way of extending a distance between the light introduction surface 101a of the light guide plate 101 and the LED 102; and a way of increasing the number of LEDs 102 to reduce the distance between the adjacent LEDs 102 (see FIG. 25). However, if these ways are employed, a disadvantage occurs, in which the size becomes large and the cost increases.
Because of this, conventionally, a backlight unit which is able to solve the above various disadvantages is proposed (e.g., see a patent document 1). Specifically, in the conventional proposed backlight unit, as shown in FIG. 26, a side surface of one corner portion of a plurality of corner portions of the light guide plate 101 is inclined with respect to other side surfaces, and the inclined surface of the light guide plate 101 is used as the light introduction surface 101a. And, the LED 102 is disposed near the corner portion where the light introduction surface 101a of the light guide plate 101 is present. According to this structure, even if only one LED 102 is used and the distance between the light introduction surface 101a of the light guide plate 101 and the LED 102 is made small, increase in dark regions (regions marked by hatching in the figure) is curbed.